Aaron Watson, a Ph.D candidate at the University of Maryland… (Baltimore Sun photo by Kim…)
As fish farming grows to feed a world hungry for protein, there's a hitch — the seas are being scoured of the little wild fish to feed the big captive ones destined for the dinner table.
Researchers in Baltimore think they may have hit upon a remedy, one that moves aquaculture closer to truly being sustainable. Working at the Institute of Marine and Environmental Technology, a branch of the University System of Maryland, scientists have developed a plant-based fish food that even finny meat eaters like striped bass gobble up.
The fish raised on such a nearly vegetarian diet also are healthier to eat, they say, with fewer of the worrisome chemical contaminants that show up in wild or even many farm-raised fish.
"You can raise fish, feed humans and not necessarily pollute the environment," said Allen Place, a professor with UM's Center for Environmental Science.
With many of the oceans' fish overfished or nearly so, farming them has become a growth industry, supplying half or more of all the fish and shellfish consumed. It's a $100 billion industry worldwide and growing 8 percent a year, according to the National Oceanic and Atmospheric Administration.
But aquaculture raises a number of environmental concerns, among them that the oceans' small "forage" fish such as menhaden could be depleted to feed all the farmed fish. About a third of all the fish harvested worldwide are not caught for human consumption, but for processing into fish meal and fish oil. Some of that goes into animal feed and into human food supplements, but two-thirds of the fish meal and nearly 90 percent of the oil is used to feed other fish, NOAA reports.
Efforts have been underway for years to find alternative, plant-based feeds for aquaculture, relying on the protein provided in such widely cultivated farm crops as corn, soybeans and wheat. While the fish-meal content in fish feed has been reduced, eliminating it altogether has proven problematic, as farm-raised fish don't eat or grow as well on diets devoid of fish meal.
Place and his graduate research assistant, Aaron Watson, at first tried feeding fish a blend of those plant products, but experienced similar difficulties. Meat-eating fish fed the plant-based food just didn't go for it — spitting it out after a taste or two — and didn't thrive.
So the UM researchers consulted aU.S. Department of Agriculturescientist who had developed a plant-based feed for farmed trout, a fresh-water fish, and adapted it for marine fish. One new ingredient that proved to be key was taurine, an amino acid that's included in energy drinks like Red Bull. Often found in nerve and muscle tissue, taurine performs a variety of biological functions and is believed to have anti-oxidant properties. While some animals can produce their own taurine, fish lack that ability, so need to get it in their diet, Place said.
The scientists then tested their taurine-laced, plant-based feed. They fed it to cobia, striped bass and Mediterranean sea bream, three fish often seen on restaurant menus, which the institute is raising in large recirculating tanks in the basement of the Columbus Center at the Inner Harbor.
The fish "went crazy for it," Place reported. Hardly any of the yellow pellets sprinkled on the water sank to the bottom, he said, the fish went after them so eagerly. The fish also grew faster on the plant-based feed than did those with diets that still contained fish meal, said Watson.
Fish raised on a plant-based diet also had fewer contaminants — a third less mercury and up to 90 percent lower levels of polychlorinated biphenyls, or PCBs. Maryland and many other states warn their residents to limit their consumption of locally caught fish because they may contain mercury, which can impair nervous system development in infants and toddlers, or PCBs, which are classified by the Environmental Protection Agency as probable carcinogens. Those chemicals even turn up in some farmed fish, likely through eating feed processed from tainted wild-caught fish.
In a bid to get completely away from feeding fish to fish, the scientists have tested a couple of entirely vegetarian recipes, trying canola oil and oil made from algae in place of the fish oil commonly found in commercial feed. Those proved as nutritious for fish and even less tainted by contaminants, but, because the replacement oils are more expensive, Place said the most viable option for now is to eliminate fish meal but keep at least some fish oil in farmed fish diets.
Meanwhile, the UM plant-based feed is getting a real-world tryout of sorts. Dave Love, with Johns Hopkins University's Center for a Livable Future, said he's feeding it to about 400 tilapia he's raising as part of an aquaponics pilot project launched earlier this year at Cylburn Arboretum in northern Baltimore.